Portable communication devices, such as cellular telephones, portable computers, personal digital assistants (PDAs), Global Navigation Satellite System (GNSS) receivers (e.g., including global positioning system (GPS), GLONASS, and BeiDou), and the like, are configured to communicate over wireless networks. Such portable communication devices may enable communication over multiple networks, and therefore include transmitters, receivers, transceivers and/or corresponding filters for connecting to common antennas, and for sending and receiving signals (e.g., radio frequency (RF) signals) over the various networks.
Acoustic filters, in particular, used in portable communication devices provide distinct advantages in reducing cost and size require, while generally improving performance Acoustic filters include acoustic resonators, such as bulk acoustic wave (BAW) resonators or surface acoustic wave (SAW) resonators. The BAW resonators may include thin film bulk acoustic resonators (FBARs) and/or solidly mounted resonators (SMRs), for example. However, BAW and SAW resonators may not provide sufficient bandwidth from intrinsic acoustic coupling for wide band application. Other types of filters, such as LC based filters, may not provide sufficiently steep roll-off. Accordingly, there is a need for band pass filters for wireless communications with very high bandwidths and, at the same time, very steep roll-off, while maintaining or improving filtering quality.